kSIST FprEN ISO 24194:2022

Solar energy - Collector fields - Check of performance (ISO/FDIS 24194:2022)

This document specifies a procedure to check a guaranteed performance of large collector fields. The collectors in the field can be glazed flat plate collectors or evacuated tube collectors.
The performance guaranteed and checked is the thermal power output of the collector field – the document specifies how to compare a measured output with a calculated one.
The document applies for all sizes of collector fields.

Sonnenenergie - Kollektorfelder - Überprüfung der Leistungsfähigkeit (ISO/FDIS 24194:2022)

Dieses Dokument legt zwei Verfahren für die Überprüfung der Leistungsfähigkeit von thermischen Sonnenkollektorfeldern fest. Bei den aufgestellten Kollektoren kann es sich um Flachkollektoren, Vakuum-Röhrenkollektoren und/oder nachgeführte konzentrierende Kollektoren handeln.
Die Überprüfung kann anhand der Wärmeleistungsabgabe des Kollektorfelds vorgenommen werden (dies wird im Hauptteil des Dokuments beschrieben).
Die Überprüfung kann auch anhand des täglichen Ertrags des Kollektorfelds vorgenommen werden (dies wird im informativen Anhang beschrieben).
Das Dokument legt für die beiden Verfahren fest, wie die gemessene Leistungsabgabe mit einer berechneten verglichen wird.
Dieses Dokument gilt für Kollektorfelder beliebiger Größe.

Energie solaire - Champs de capteurs - Vérification de la performance (ISO/FDIS 24194:2022)

Sončna energija - Polja sprejemnikov sončne energije - Preverjanje zmogljivosti (ISO/FDIS 24194:2022)

General Information

• Status: Not Published
• Public Enquiry End Date: 04-Jul-2021
• ICS: 27.160 - Solar energy engineering
• Technical Committee: TOP - Thermal insulation
• Current Stage: 5020 - Formal vote (FV) (Adopted Project)
• Start Date: 12-Apr-2022
• Due Date: 31-May-2022
• Ref Project: FprEN ISO 24194 - Solar energy - Collector fields - Check of performance (ISO/FDIS 24194:2022)

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN ISO 24194:2021
01-julij-2021
Sončna energija - Polja sprejemnikov sončne energije - Preverjanje zmogljivosti
(ISO/DIS 24194:2021)
Solar energy - Collector fields - Check of performance (ISO/DIS 24194:2021)
Sonnenenergie - Kollektorfelder - Überprüfung der Leistungsfähigkeit (ISO/DIS
24194:2021)
Energie solaire - Champs de capteurs - Vérification de la performance (ISO/DIS
24194:2021)
Ta slovenski standard je istoveten z: prEN ISO 24194
ICS:
27.160 Sončna energija Solar energy engineering
oSIST prEN ISO 24194:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO 24194:2021
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oSIST prEN ISO 24194:2021
DRAFT INTERNATIONAL STANDARD
ISO/DIS 24194
ISO/TC 180/SC 4 Secretariat: SAC
Voting begins on: Voting terminates on:
2021-04-14 2021-07-07
Solar energy — Collector fields — Check of performance
ICS: 27.160
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 24194:2021(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. ISO 2021
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oSIST prEN ISO 24194:2021
ISO/DIS 24194:2021(E)
ISO/DIS 24194:2021(E)
Contents

Foreword ................................................................................................................................................................ iv

Introduction ........................................................................................................................................................... v

1 Scope ................................................................................................................................................................. 1

2 Normative references ................................................................................................................................. 1

3 Terms and definitions ................................................................................................................................ 1

4 Symbols............................................................................................................................................................ 2

5 Procedure for checking the power performance of solar thermal collector fields ............. 5

5.1 Stating an estimate for the thermal power output of a collector field ..................................... 5

5.2 Calculating power output .......................................................................................................................... 5

5.2.1 Equation 1 ................................................................................................................................................ 6

5.2.2 Equation 2 ................................................................................................................................................ 7

5.2.3 Equation 3 ................................................................................................................................................ 7

5.3 Stating a performance estimate .............................................................................................................. 7

5.4 Restrictions on operating conditions ................................................................................................... 7

5.5 Shadows ........................................................................................................................................................... 8

5.5.1 Shadows on fixed collectors in rows ............................................................................................... 8

5.5.2 Shadows on one-axis tracking collectors in row ........................................................................ 9

5.6 Collector incidence angle ....................................................................................................................... 11

5.7 Example of setting up an equation for calculating performance estimate .......................... 12

5.8 Determination of potential valid periods ........................................................................................ 12

5.9 Checking performance estimates ........................................................................................................ 13

5.9.1 Checking collector field performance ......................................................................................... 13

6 Measurements needed ............................................................................................................................ 14

6.1 Requirements on measurements and sensors ............................................................................... 16

6.1.1 Time ......................................................................................................................................................... 16

6.1.2 Solar radiation measurement ........................................................................................................ 17

6.1.3 Temperature measurements ......................................................................................................... 18

6.1.4 Flow rate measurement ................................................................................................................... 19

6.1.5 Power measurement / calculation ............................................................................................... 19

6.1.6 Measurement of wind speed ........................................................................................................... 19

6.2 Valid data records ..................................................................................................................................... 19

Annex A 1 (informative) Recommended reporting format - Power Method ............................. 21

Annex A 2 (informative) Recommended reporting format - Daily Yield Method ..................... 24

Annex B 1 (informative) Recommended format for stating the estimated performance-

Power Method ...................................................................................................................................... 25

Annex C (informative) Procedure for checking the daily performance of solar thermal

collector fields ..................................................................................................................................... 26

COPYRIGHT PROTECTED DOCUMENT

Bibliography ....................................................................................................................................................... 30

© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
© ISO #### – All rights reserved iii
ii © ISO 2021 – All rights reserved
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oSIST prEN ISO 24194:2021
ISO/DIS 24194:2021(E)
Contents

Foreword ................................................................................................................................................................iv

Introduction ........................................................................................................................................................... v

1 Scope ................................................................................................................................................................. 1

2 Normative references ................................................................................................................................. 1

3 Terms and definitions ................................................................................................................................ 1

4 Symbols............................................................................................................................................................ 2

5 Procedure for checking the power performance of solar thermal collector fields ............. 5

5.1 Stating an estimate for the thermal power output of a collector field ..................................... 5

5.2 Calculating power output .......................................................................................................................... 5

5.2.1 Equation 1 ................................................................................................................................................ 6

5.2.2 Equation 2 ................................................................................................................................................ 7

5.2.3 Equation 3 ................................................................................................................................................ 7

5.3 Stating a performance estimate .............................................................................................................. 7

5.4 Restrictions on operating conditions ................................................................................................... 8

5.5 Shadows ........................................................................................................................................................... 8

5.5.1 Shadows on fixed collectors in rows ............................................................................................... 8

5.5.2 Shadows on one-axis tracking collectors in row ........................................................................ 9

5.6 Collector incidence angle ....................................................................................................................... 12

5.7 Example of setting up an equation for calculating performance estimate .......................... 12

5.8 Determination of potential valid periods ........................................................................................ 13

5.9 Checking performance estimates ........................................................................................................ 13

5.9.1 Checking collector field performance ......................................................................................... 13

6 Measurements needed ............................................................................................................................ 14

6.1 Requirements on measurements and sensors ............................................................................... 16

6.1.1 Time ......................................................................................................................................................... 16

6.1.2 Solar radiation measurement ........................................................................................................ 17

6.1.3 Temperature measurements ......................................................................................................... 18

6.1.4 Flow rate measurement ................................................................................................................... 19

6.1.5 Power measurement / calculation ............................................................................................... 19

6.1.6 Measurement of wind speed ........................................................................................................... 20

6.2 Valid data records ..................................................................................................................................... 20

Annex A 1 (informative) Recommended reporting format - Power Method.............................. 21

Annex A 2 (informative) Recommended reporting format - Daily Yield Method ..................... 24

Annex B 1 (informative) Recommended format for stating the estimated performance-

Power Method ...................................................................................................................................... 25

Annex C (informative) Procedure for checking the daily performance of solar thermal

collector fields ..................................................................................................................................... 26

Bibliography ....................................................................................................................................................... 30

© ISO 2021 – All rights reserved iii
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oSIST prEN ISO 24194:2021
ISO/DIS 24194:2021(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO

collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any

patent rights identified during the development of the document will be in the Introduction and/or on

the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the World

Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 180, Solar energy, Subcommittee SC 4,

Systems - Thermal performance, reliability and durability.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
iv © ISO 2021 – All rights reserved
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oSIST prEN ISO 24194:2021
ISO/DIS 24194:2021(E)
Introduction

This document defines procedures for checking the performance of solar thermal collector fields.

Measured performance is compared with calculated performance - and conditions for compliance are

given.
Two levels for accuracy in the checking can be chosen:

• Level I - giving possibility for giving a very accurate estimate (with low safety factor) - but with

requirements for use of expensive measurement equipment.

• Level II - allowing for a less accurate estimate (with higher safety factor) - but possibility to use less

expensive measurement equipment..
© ISO 2021 – All rights reserved v
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oSIST prEN ISO 24194:2021
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oSIST prEN ISO 24194:2021
DRAFT INTERNATIONAL STANDARD ISO/DIS 24194:2021(E)
Solar energy — Collector fields — Check of performance
1 Scope

This document specifies two procedures to verify the performance of solar thermal collector fields. The

collectors in the fields can be glazed flat plate collectors, evacuated tube collectors and/or tracking,

concentrating collectors.

The check can be done on the thermal power output of the collector field - this is described in the main

part of the document.

The check also be done on the daily yield of the collector field - this is described in informative annex.

The document specifies for the two procedures how to compare a measured output with a calculated one.

The document applies for all sizes of collector fields.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 9060, Solar energy — Specification and classification of instruments for measuring hemispherical

solar and direct solar radiation
ISO 9488, Solar energy — Vocabulary
ISO 9806, Solar energy — Solar thermal collectors — Test methods
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 9488 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
reflector
surface intended for reflecting radiant energy
3.2
transversal plane

plane defined by the normal to the plane of the collector and the line orthogonal to the concentrator axis,

or the shortest symmetry line for flat biaxial geometries
© ISO 2021 – All rights reserved 1
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oSIST prEN ISO 24194:2021
ISO/DIS 24194:2021(E)
4 Symbols
A Gross area of collector as defined in the ISO 9488 m
A Gross area of collector field m
a Heat loss coefficient at (ϑ − ϑ ) = 0 W/(m K)
1 m a
2· 2
a Temperature dependence of the heat loss coefficient W/(m K )
a Wind speed dependence of the heat loss coefficient J/(m K)
a Sky temperature dependence of the heat loss coefficient —
a Effective thermal capacity. In some literature and data sheets J/(m K)
denoted C
eff
a Wind speed dependence of the zero-loss efficiency s/m
2· 4
a Wind speed dependence of IR radiation exchange W/(m K )
2· 4
a Radiation losses dependence W/(m K )
b Collector efficiency coefficient (wind dependence) s/m
C Effective thermal capacity of collector J/K
C Geometric concentration ratio —
c Specific heat capacity of heat transfer fluid J/(kgK)
c Specific heat capacity of heat transfer fluid at the collector inlet J/(kgK)
f,i
c Specific heat capacity of heat transfer fluid at the collector outlet J/(kgK)
f,e
DNI Solar radiation received per unit area by a surface that is always W/m
held perpendicular (or normal) to the rays that come in a straight
line from the direction of the sun at its current position
E Longwave irradiance (λ > 3 μm) W/m
Safety factor taking into account heat losses from pipes etc. in the
collector loop.
Safety factor taking into account measurement uncertainty.
Safety factor for other uncertainties e.g. related to non-ideal
conditions such as non-ideal flow distribution and unforeseen heat
losses - and uncertainties in the model/procedure itself.
f f = f · f · f -
safe safe P U O
f Shading factor -
G Gap in between adjacent collectors m
G Hemispherical solar irradiance on the plane of collector W/m
hem
G Direct solar irradiance (beam irradiance) on the plane of collector W/m
G Diffuse solar irradiance on the plane of collector W/m
H Total daily irradiation sum on collector plane without shadow kWh/m
hem
2 © ISO 2021 – All rights reserved
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oSIST prEN ISO 24194:2021
ISO/DIS 24194:2021(E)
Solar altitude angle. sin h = cos θ
h Minimum solar altitude angle °
min
H Height of the shaded area m
K (θ ,θ ) Incidence angle modifier for hemispherical solar radiation —
hem L T
K (θ ,θ ) Incidence angle modifier for direct solar irradiance —
b L T
K Incidence angle modifier in the longitudinal plane —
K Incidence angle modifier in the transversal plane —
K Incidence angle modifier for diffuse solar radiation —
L Length of a collector m
L Overall Length of the pipe system without collectors m
pipe
L Length of the shaded area m
𝑚𝑚̇ Mass flow rate of heat transfer fluid kg/s
N Number of collectors in a row -
Coordinate of the point C on the x-axis (C is the point that would -
P reach the shadow formed by the top of the sun facing side of a
collector row if it were unobstructed)
P Coordinate of the point C on the y-axis -
Measured power output W
𝑄𝑄̇R
measured
̇Estimated power output W
𝑄𝑄 R
estimate
Q Daily capacity heat losses of solar thermal system J
cap,d
Q Daily yield estimation of solar thermal system J
estimate-sys,d
Q� Daily average gross power output collector field W
estimate-col,d
Q Daily yield measurement of the heat meter J
HM,d
Q� Daily average heat losses of piping W
pipe,d
q Empirical specific heat loses per m pipe W/m
l-pipe
S Spacing center to center in between adjacent rows m
T Absolute temperature K
t Time s
t Time start of measurement s
t Time end of measurement s
u Surrounding air speed (wind speed) m/s
u' Reduced surrounding air speed u' = u - 3 m/s m/s
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oSIST prEN ISO 24194:2021
ISO/DIS 24194:2021(E)
V Fluid capacity of the collector m
m /s
𝑉𝑉̇ Volumetric flow rate
Volumetric flow rate at the outlet of the solar collector m /s
𝑉𝑉̇
𝑒𝑒
𝑉𝑉̇ Volumetric flow rate at the inlet of the solar collector m /s
𝑖𝑖
V Volume of the pipe system without collectors l
pipe
W Width of a collector
Δt Time interval s
ΔT Temperature difference between fluid outlet and inlet (ϑ - ϑ ) K
e i
β Slope (or tilt), the angle between the plane of the collector and the
horizontal.
Note: For collectors rotating around a North-South axis, β is positive
in the morning when facing eastwards - and negative in the
afternoon when facing westwards
γ Surface azimuth angle, the deviation of the projection on horizontal °
plane of the normal to the surface from the local meridian, with
zero due south, east negative and west positive
γ Solar azimuth angle, the angular displacement from south of the °
projection of beam radiation on the horizontal plan, east negative
and west positive
δ Declination, the angular position of the sun at solar noon with °
respect to the plane of the equator, north positive.
Latitude, the angular location north or south of the equator, north °
positive
η Collector efficiency based on beam irradiance G —
b b
η Collector efficiency based on hemispherical irradiance G —
hem hem
η Peak collector efficiency (η at ϑ − ϑ = 0 K) based on beam —
0,b b m a
irradiance G
η Peak collector efficiency (η at ϑ − ϑ = 0 K) based on —
0,hem 0,hem m a
hemispherical irradiance G
hem
𝜂𝜂 Collector efficiency, with reference to mass flow 𝑚𝑚̇ —
ℎ𝑒𝑒𝑒𝑒,𝑒𝑒̇𝑖𝑖
𝑖𝑖
ω Hour angle, the angular displacement of the sun east or west of the °
local meridian due to rotation of the earth on its axis at 15 ° per
hour; morning negative, afternoon positive
θ Angle of incidence °
θ Longitudinal angle of incidence: angle between the normal to the °
plane of the collector and incident sunbeam projected into the
longitudinal plane
θ Transversal angle of incidence: angle between the normal to the °
plane of the collector and incident sunbeam projected into the
transversal plane
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oSIST prEN ISO 24194:2021
ISO/DIS 24194:2021(E)
θ Zenith angle, the angle between the vertical and the line to the sun, °
that is, the angle of incidence of beam radiation on a horizontal
surface. cos θ = sin h
ϑ Ambient air temperature °C
ϑ Measured ambient air temperature °C
ϑ Ambient air temperature for the standard stagnation temperature °C
ϑ Collector outlet temperature °C
ϑ Collector inlet temperature °C
ϑ Mean temperature of heat transfer fluid in collector loop °C
ϑ Maximum operating temperature °C
max_op
ρ Density of heat transfer fluid at collector inlet temperature kg/m
ρ Density of heat transfer fluid at heat exchanger inlet temperature kg/m
i,sec
2 4
σ Stefan-Boltzmann constant W/(m K )
5 Procedure for checking the power performance of solar thermal collector
fields
5.1 Stating an estimate for the thermal power output of a collector field

The estimated power output of the collector array is given as an equation depending on collector

parameters according to ISO 9806 and operating conditions. The measured power shall comply with the

corresponding calculated power according to this equation. Measured and calculated power are only

compared under some specific conditions to avoid too large uncertainties - see section 5.4.

The estimate can be given for fields of combined collector types - e.g. single glazed and double-glazed:

• If size, inlet and outlet temperatures are available for each field of collectors of same type,

estimates can be given for each of these fields.

• An overall estimate for fields with two or more similar collector types can be given choosing

representative collector parameters.

Note: Similar types are e.g. flat plate collectors with single glazing and flat plate collectors with double

glazing.

When giving the estimate it shall be stated if it shall be checked according to levels of accuracy I or level

II (see Introduction and section 6.1).
5.2 Calculating power output

Depending on collector type and solar measurements there are three options for equations:

a) eq. 1: Simple equation using total radiation on the collector plane, valid for:

• Non-concentrating collector only

b) eq. 2: A more advanced equation using direct and diffuse radiation, valid for:

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oSIST prEN ISO 24194:2021
ISO/DIS 24194:2021(E)
• Non-concentrating collector
• Concentrating collectors with low concentration ratio C < 20

c) eq. 3: Equation using direct radiation specifically for concentrating collectors with high

concentrating ratio, valid for:
• Focussing collectors with concentration ratio C ≥ 20

The estimate is given by stating the equation to be used for calculating the power output, including

specific values for the parameters in equation. The three possible equations are given in the next three

sub-sections.

The collector module efficiency parameters η0,hem, η0,b, K (θ , θ ), K , a , a , a and a should be based

b L T d 1 2 5 8

on certified test results. When an estimate is given, it shall always be stated which equation shall be used

for checking the performance:

a) Simple check, using total radiation on the collector plane when checking the power output (ISO

this standard, eq 1).

b) Advanced check, using direct and diffuse radiation on collector plane when checking the power

output (ISO this standard, eq 2).

c) Advanced check, using only direct radiation on collector plane when checking the power output

(ISO this standard, eq 3).

Note: Always be very careful if the collector area given is the gross area or the aperture area - and if collector

parameters given are related to the gross area or the aperture area.
5.2.1 Equation 1

A simple power performance estimate for non-concentrating collectors is given with eq. (1):

R = A ·[η G - a (ϑ - ϑ ) - a (ϑ - ϑ ) - a (dϑ /dt)] · f (1)
𝑄𝑄
estimate GF 0,hem hem 1 m a 2 m a 5 m safe
ϑ is mean value of collector in - and outlet temperatures.

Using eq. 1 will normally give bigger uncertainty than using eq. 2 as incidence angle modifiers for the

collector are not considered.

f is chosen considering potential influences from pipe heat loss, measurement uncertainties, model

safe
uncertainties etc..

f is divided into factors considering specific influences. As an example, f could be calculated from

safe safe
f = f · f · f , where:
safe P U O

Safety factor considering heat losses from pipes etc. in the collector loop. To be estimated

fP:
based on an evaluation of the pipe losses - normally only a few %.

Safety factor considering measurement uncertainty. To be estimated - with the requirem

...